Recycling of wastepaper is a key to survival of pulp and paper industries. The driving forces are limited by space for landfills, prevention of forests, and consumer pressure and legislation for recycled content in paper products. To produce good quality recycled paper requires, among other, the removal of ink from wastepapers which is commonly recognized as wastepaper deinking. Various technologies are available for doing this, which essentially consists of two steps: detaching ink from fiber and separating the suspended ink particles from the pulp slurry. For each step a variety of options are open; ink dispersion is usually achieved in the repulping step by the addition of deinking chemicals mostly in an alkaline medium, while ink separation is effected by screening, washing or flotation.
During recent years flexographic printing has been developed beyond the printing of pakaging materials and is an option for newspaper printing. Flexographic inks are water-based, providing printing and environmental benefits, but their presence reduce deinking quality by froth flotation and results in a more difficult effluent classification from washing devices. A very similar problem is encountered for inkjet-printed officewastes. Sales of inkjet printers are increasing rapidly due to more and more use of network computers, electronic mail etc. Pulping of papers printed in Deskjet printer, utilizing a liquid ink system, produces smaller particles than laser printers or photocopiers. In fact, on pulping, the deskjet-printing inks which are essentially dyes dissolved in water and glycols, totally disperse in aqueous repulping medium to produce a uniformly grey stock.
In practice segregation of wastepaper based on the type of printing is impossible. In most cases, wastepapers containing newsprints printed with offset and lithography are contaminated with flexo-printed newsprints. Similarly, officewastes containing toner based printed papers are contaminated with inkjet-printed officewastes. Although successful deinking technologies by froth flotation are available for offset and lithography printed newsprints, a flexography or inkjet printed paper contamination into other printed paper is causing severe deinking problem for the reason mentioned above.
The present invention simplifies the deinking of flexo- and inkjet-printed papers contaminated wastepaper mixtures using repulping and froth flotation processes by treating a repulped slurry in aqueous medium with a surface active polymer composition in presence or absence of a conventional surfactant to agglomerate small ink particles to a size range suitable for flotation and finally removing those agglomerated inks by creating air bubbles under constant agitation from the said repulped slurry.